NCERT Solutions Class 12 Biology Chapter 4 Principles of Inheritance and Variation

As per the revised curriculum of CBSE Syllabus 2023-24, this chapter, previously known as Chapter 5, has now been renumbered as Chapter 4. Stay updated with the latest changes in the curriculum.

Principles of Inheritance and Variation Class 12 NCERT Solution is all about the process and principle of Principles of Inheritance and Variation. These NCERT Solutions are prepared by our Top Biology Experts in order to take care of all Important Topics that might be asked in the upcoming examination 2023. So, Students can also refer to these solutions for their final Examination preparation.

This Class 12 Biology Chapter 4 Principle of Inheritance and Variations NCERT Solutions are carefully developed using easy-to-understand language while adhering to the guidelines for solving NCERT Solutions for Class 12. Working through these solutions can be highly beneficial for students in their board exams, as well as in preparing for future competitive Exams.

Principles of Inheritance and Variation Class 12 Biology Chapter 4

NCERT Solution for Class 12 Principle of Inheritance and Variation explains the inheritance of genes from parents to offspring. About Mendel’s discoveries and other important concepts of inheritance. Revise the basic concepts of Principles of Inheritance and Variation for quick revision and class notes.

Q1: Mention the advantages of selecting a pea plant for the experiment by Mendel.

Answer:

Gregor Mendel demonstrated traits of inheritance inherited by progeny from their parents. He selected a pea plant for this experiment for several reasons which  are mentioned below:

• Pea plants have seven distinct characteristics with easily identifiable characteristics including tall and short stature. Wrinkled/round seeds, yellow/green pods, white/purple flowers, etc.
• Since they have bisexual flowers, they can easily go through self-pollination. This is the reason why pea plants are able to produce progeny with the generation of the same characteristic after generation.
• Cross-pollination is easily accomplished through emasculation, which involves plucking the stamen of the flower without disturbing the pistil.
• Due to the annual nature of the plant, multiple generations may be studied within a short period.
• These plants have a life span of 3 months in which they produce lots of seeds in a single generation.

Q2: Differentiate between the following:

• (a) Dominance and Recessive
• (b) Homozygous and Heterozygous
• (c) Monohybrid and Dihybrid

Answer: 

(a) Dominance and Recessive

Dominance	Recessive
An allele or dominant factor expresses itself in the presence or absence of a recessive trait,	Only in the absence of a dominant characteristic does a recessive trait express itself.
For Instance: In a pea plant, round seeds and violet flowers both are dominant traits.	For Instance: In a pea plant, white flower, or dwarf plant, both are recessive traits.
Dominant characters are those who appear in the F1 generation	The F2 generation consists of the recessive traits

(b) Homozygous and Heterozygous

Homozygous	Heterozygous
Homozygous have a specific trait, it consists of two similar alleles.	For a specific trait, heterozygotes have two different alleles.
It is produced only one type of gametes because they are identical to each other.	It is produced one or two different types of gametes because they consist of two different alleles.
If an individual is homozygous, they only have one of the two alleles present – never both. Example: TT or TT	if an individual is heterozygous, they have both dominant and recessive alleles. example: Tt
They are true-breeding for a particular trait and produce offspring with identical genotypes and phenotypes upon selfing.	heterozygous are not true-breeding and produce progeny with three genotypes and mostly two or at times three phenotypes.

(c) Monohybrid and Dihybrid

Monohybrid	Dihybrid
“A monohybrid cross is a hybrid of two individuals with identical genotypes, resulting in opposite phenotypes for a certain genetic characteristic.	A dihybrid cross is a hybrid made up of two organisms that are heterozygous for two separate traits in both of them.
It is a crossing over between parents differing in only one pair of opposing characters.	It is a crossing over between parents differing in two pairs of opposing characters.
In this experiment, two pea plants that had opposite traits (a short plant and a tall plant. they found that the offspring of the first generation were tall and were called F1 offspring	In this experiment, He crossed over between wrinkled-green seeds and round-yellow seeds and obtained that all the first-generation progeny (F1 progeny) were round-yellow.

Q3: A diploid organism is heterozygous for 4 loci, how many types of gametes can be produced?

Answer:

A locus is a fixed point on a chromosome that is occupied by one or more genes. For each member of an allele pair, heterozygous individuals have different alleles. Consequently, a diploid individual who is heterozygous with four loci has four different opposing traits at four different loci. which is heterozygous for 4 loci, then 24 is that 2 x 2 x 2 x 2 = 16 types of gametes can be produced if the genes are not paired as there are two possibilities for each heterozygous pair of genes

Example:  If an entity has heterozygosity at four loci for four distinct traits, such as Aa, AB, Oo, and Ff, they will split into eight separate gametes during meiosis

Q4: Explain the Law of Dominance using a monohybrid cross.

Answer: 

Law of Dominance:

As per the law of dominance, a hybrid progeny will only inherit the dominant trait in the phenotype. The allele whose characters are expressed over the other allele is referred to as the dominant allele, and the recessive traits while the alleles that caused the trait are called the dominant traits. Dominant characters are those who appear in the F1 generation. The F2 generation consists of recessive traits.

Example: “In this experiment, Mendel selected pea plants with two opposite characters, a short plant, and a tall plant, and made a cross between them. They found that the offspring of the first generation were tall and were called F1 offspring. Therefore, in the F1 generation, the traits that are dominant, He then crossed the F1 progeny and produced both tall and short plants in a ratio of 3:1.

Q5: Define and design a test cross.

Answer:

                                                                            F1   x  recessive parent

                                           F1 generation          Tt           X           tt

                                                                            Tall              Dwarf recessive

                                                      Gametes:      T                t                 t             t

                                                    Offsprings:      Tt               Tt                   tt            tt

                                                                                       Ratio: 1:1

Test Cross: A test cross can be crossed between an F1 individual that has a dominant phenotype with its homozygous recessive parent. This test cross can be utilized to decide if an individual displaying dominant traits is homozygous or heterozygous. If the test cross’s offspring has a 1:1 Dominant: Recessive ratio, the unknown plant is heterozygous.  if all of the offspring are dominant, however, then the unknown plant is homozygous.

Q6: Using a Punnett Square, work out the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus.

Answer:

We can observe that the male generates two types of gametes, W and w, whereas the female only produces one type of gamete, w when heterozygous male guinea pigs (Ww) with black coats are crossed with homozygous female guinea pigs (ww) with white coats. 

Using the Punnett square, we can observe that the genotypic and phenotypic ratios in the (F1)generations are the same, or 1:1.

                                                                   Parents        WW   x  Ww

                                                                                (Female)  x   (Male)

                                                               Gametes:      W              W              W          w

                                                            Offsprings:      WW             Ww           WW      Ww

                                                                                Ratio: 1:1

Q7: When a cross is made between a tall plant with yellow seeds (TtYy) and a tall plant with green seeds (Ttyy), what proportions of phenotype in the offspring could be expected to be

• (a) tall and green?
• (b) dwarf and green

Answer:

(a) tall and green.

	TY	Ty	tY	ty
TY	TTYY	TTYy	TtYY	TtYy
Ty	TTYy	TTyy	TtYy	Ttyy
tY	TtYY	TtYy	ttYY	ttYy
ty	TtYy	Ttyy	ttYy	ttyy

The phenotype of tall plants with green see ratio is- 3:8

Q8:  Two heterozygous parents are crossed. If the two loci are linked what would be the distribution of phenotypic features in F1 generation for a dihybrid cross?

Answer:

The co-existence of two or more genes on the same chromosome is referred to as linkage. If the genes are located near to each other, and on the same chromosome, they are acquired simultaneously and are known as linked genes. The result is as follows if the linkage is present between two heterozygous parents:

Parents           BbLl x BbLl

Genotype:   BBbb:BbLi: BbLi: LLII

                   Blue: long: Blue: long

Because the genes are totally connected, the phenotype in F1 may display parental traits in any feasible way. The blue long type of genotype in the aforementioned example can be seen in progeny with any of the available genotypes in F1. The ancestral combination will, however, be more numerous than the more recent combinations, which are few in number, if there is an imperfect linkage.

Q9: Briefly mention the contribution of T.H. Morgan to genetics.

Answer:

The Chromosomal Theory of Inheritance was originally developed by Sutton and Boveri in the year 1902. This theory was established by Thomas Hunt Morgan, that studied fruit flies (Drosophila melanogaster). T H Morgan is an American geneticist and is considered the “father of experimental genetics” because his work won the Nobel Prize in 1933. He discovered the theory of linkage, crossing over, sex linkage, crisscross inheritance, linkage maps, mutation of genes, and many other experiments. He is referred to as a fly man of A because of choosing fruit fly (Drosophila melanogaster) as experiment material for genetics

• The two alleles of a gene are situated on the homologous pair of chromosomes at the same position where chromosomes exist as a homologous pair.  
• chromosomes separate during meiosis in the process of gametogenesis. Chromosomes are separate and assort independently.
• The chiasma produces crossing over, according to Morgan’s chiasma-type hypothesis.
• He discovered that the frequency of recombination between two connected genes is inversely correlated with their separation.

Q10: What is pedigree analysis? Suggest how such an analysis can be useful.

Answer:

Pedigree Analysis supports examining the risk of getting a genetic disorder in the progeny by studying the pattern of inheritance of a specific feature present in various generations of an individual. Pedigree analysis is the analysis of multiple generations of a family, used on both humans and domesticated animals.

The Importance of pedigree analysis

• It serves as a potent tool that can be utilized to determine the inheritance of a specific trait, disease, or abnormality.
• The possibility of having children with genetic disorders including color blindness, hemophobia, thalassemia, sickle cell anemia, etc. is something that genetic counselors can assist couples to consider.
• The analysis is supported by indicating the origination of a feature and its flow in ancestors.
• It is supportive in suggesting that Mendel’s concepts can be applied to human genetics with some modification, like-quantitative inheritance, sex-related linkage, and characters.

Q11: How is sex determined in human beings?

Answer:

Sex determination is a process that determines the sexual characteristics of an organism or progeny. It supports to the decision of whether the organism will be male or female, which are the two types of sexes.  The X or Y is two sexes. Chromosomal Sex Determination Humans consist of  23 pairs of chromosomes and 46  single chromosomes. Out of these 23 pairs, 22 pairs are referred to as autosomes whereas 1 pair is called the sex chromosome. This one pair decided the sex of an individual. scientist Germann Henking conducted the initial research on this in 1891. he was researching a different nuclear material, which he first recognized. The X chromosome was given that name. The studies on the sex determination of both sexes in all animals began from this point. Types of Sex Determination The XX-XY system is seen in humans, where XX is the female and XY is the male. This is also seen in a few insects.

In the process of fertilization, if the sperm consisting of an X chromosome fertilizes the egg, then the producing progeny would be a female (XX) and if the sperm consisting of a Y chromosome fertilizes the egg, then the producing progeny would be a male (XY). As a result, the sex ratio i.e. developed in the offspring is 1:1. The chromosomal method for determining sex, heterogenesis, can occur either in males or in females..

Q12: A child has blood group O. If the father has blood group A and the mother’s blood group is B, work out the genotypes of the parents and the possible genotypes of the other offspring.

Answer:

In humans, the blood group characteristics are controlled by a group of three alleles referred to as IA, IB, and i. if the alleles IA and IB are similarly dominant, and allele i is recessive to the other alleles.

The blood group will be	Individuals with Genotype
A	IA, IA, IA, I
B	IB, IB, IB, i
AB	IA, IB
O	ii

If the father has blood group A and the mother’s blood group is B,

                                                          Parents:    IAIA          X           IBIB

                                                                          Father                 Mother  

                                                          Gametes:      IA                           IB            

                                                           Offsprings:     IAIB

                                                          Offspring Blood Group:  AB Blood Group

A child has blood group O,If the father has blood group A and the mother’s blood group is B

                                                         Parents:    IAi       X           IBi

                                                                         Father                 Mother  

                                                         Gametes:    IA      i              IB       i    

                                                          Offsprings:     IAIB              ii

                                                         Offspring Blood Group:  IAIB Consists of AB Blood Group

                                                                                                 ii Consist of O Blood Group

Q13: Explain the following terms with an example.

• (a) Co-dominance
• (b) Incomplete dominance

Answer:

(a) Co-dominance:

It is a phenomenon of two alleles that do not have a dominant-recessive connection and both express themselves in the organism. ABO blood grouping in humans is regulated by gene I. There are three alleles in the gene: IA, IB, and i. Any two of the three alleles IA and IB are dominant over i in any individual. The plasma membrane of red blood cells consists of sugar polymers that protrude from its surface and this type of sugar is controlled by genes. Due to codominance, both IA and IB express their respective types of sugars when they are together.

(b) Incomplete dominance:

It is a post-Mendelian discovery. Incomplete dominance is the occurrence of either of the two alleles being dominant so that the expression in the heterogenous is a good combination or intermediate between the expressions of the two alleles.. In snapdragon (Mirabilis jalapa), there are two types of pure breeding plants, red flowered and white flowered. On crossing the two, F1 plants possess pink flowers. On selling them, the F2 generation has 1 red: 2 pink: 1 white. The pink flower is due to incomplete dominance.

Q14: What is point mutation? Give one example.

Answer:

Mutation: Any modification in the sequence of DNA is referred to as a mutation. Viable mutations get acquired from one generation to the next generation. A mutation changes that affect both the genotype and the phenotype of an organism. Although it is related to many diseases, not all mutations are dangerous. Any additions, deletions, duplications, or substitutions, and many other things.

The change in the shape of the RBCs from bilobed discs too long sickle-shaped formation is caused due to changing of a single nitrogen base guanine to adenine at the sixth codon of the β-globin sequence of the hemoglobin components.  The normal RBC is biconcave, resembling a flexible disc-like structure that makes it easier for the cells to pass through both large and small blood capillaries in order to transport oxygen. A blockage that slows or stops blood flow results from sickle-shaped RBCs because they are hard, elongated, and non-flexible in structure. This condition is known as sickle cell anemia.

Q15: Who proposed the chromosomal theory of inheritance?

Answer:

The Chromosomal Theory of Inheritance was originally developed by Sutton and Boveri in the year 1902. This theory was established by Thomas Hunt Morgan, that studied fruit flies (Drosophila melanogaster).

Q16: Mention any two autosomal genetic disorders with their symptoms.

Answer:

There are several disorders in the human being that are acquired and caused due to mutation in the gene or alteration in chromosomes. Hence these disorders are caused by damage to genes present in autosomes. A few examples of autosomal genetic disorders are Down syndrome, sickle cell anemia, Patau syndrome, and phenylketonuria.

Down’s syndrome is caused by chromosome 21 trisomy.

• Mental impairment, 
• small stature, 
• a wrinkled tongue 
• a partially open mouth short neck and flat hands
• wide forehead

Sickle cell Anemia Symptom

• The change in the shape of the RBCs from bilobed discs too long sickle-shaped formation is caused due to changing of a single nitrogen base guanine to adenine at the sixth codon of the β-globin sequence of the hemoglobin components. Due to reduced oxygen tension, 
• These sickle-shaped RBCs break down more quickly than the regular ones, which results in anemia.

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FAQs on Principles of Inheritance and Variation Class 12 NCERT Solution

Q1: What is the name of chapter 4 of NCERT class 12 Biology?

Answer:

Class 12 Biology Chapter 4 name is Principles of Inheritance and Variation which tells about mendelism, the inheritance of genes from parents to new offspring.

Q2: Where can I find NCERT solutions for the Class 12 Biology Chapter 4?

Answer:

NCERT solutions for Class 12 Biology Chapter 4 can be found on various online platforms such as the official NCERT website, GeeksForGeeks, and more.

Q3: Why are NCERT Solutions for Class 12 Biology Chapter 4 beneficial for the students??

Answer:

The benefits of using the NCERT Solutions for Class 12 Biology Chapter 4 are:

• Completely solved answers for all the questions present in the NCERT textbook are available in PDF format.
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